1. Field of the Invention
The present invention relates to a shift control device of a hydraulic control system for an automatic transmission system. More particularly, it relates to a shift control device of a hydraulic control system that may perform a five-speed shift control and improve shift sense and speedy response ability of operating elements, and includes a means for preventing a reverse when a shift lever is shifted to a reverse operation of the vehicle "R" range during a forward running.
2. Description of the Related Art
A conventional automatic transmission for a vehicle has a torque converter and a multiple stage transmission gear mechanism connected with the torque converter, which includes a hydraulically-actuated friction member for selecting one among a plurality of gear stages of the transmission gear mechanism in accordance with vehicle operating conditions.
A hydraulic pressure generated by an oil pump is provided to the friction members for transmitting dynamics of the multiple stage transmission gear mechanism via the shift valves of the hydraulic control system.
The commonly-used automatic transmission for a vehicle has the torque converter which generally includes a pump impeller connected with an engine output shaft to be driven thereby, a turbine runner connected with an input shaft of the transmission system in and a stator disposed between the pump impeller and the turbine runner. According to this structure, the hydraulic fluid is circulated by the engine-driven pump impeller through the turbine runner with the aid of the stator which functions to deflect the hydraulic fluid from the turbine runner to a direction where fluid flow does not disturb a rotation of the pump impeller when the fluid flows into the pump impeller. An automatic shift is made by an operation of the friction members such as clutches or a kick-down brake at each shift change. The above friction members selectively operate due to the change in the direction of fluid flow by a plurality of valves of the hydraulic control device. Besides, a manual valve, a port of which is converted by selecting a position of a selector lever, is designed to be supplied with a fluid pump and to supply the fluid to a shift control valve. The shift control valve provides a hydraulic pressure to one or more than one shift valve among a plurality of shift valves according to an ON-OFF operation of a shift control solenoid valve controlled by a transmission control unit, and controls these shift valves to form a line.
Such a hydraulic control system is disclosed in U.S. Pat. Nos. 4,776,240, 4,870,877 and 5,131,298.
Neither a method for improving shift sense nor a method for ensuring rapid response ability is proposed in these prior art techniques. Besides, they do not propose a method for preventing the driving "D" range from being shifted to the reverse "R" range.
A valve spool of the shift valve is elastically supported by an elastic member, and has a problem that the size of the valve body is enlarged as large as the space where the elastic member is installed.